1. Field of the Invention
The present invention relates to a lens barrel cam mechanism capable of extending and retracting a lens barrel by a cam mechanism and a method of manufacturing a rotary member suitable for use with such cam mechanism.
2. Description of the Related Art
Cited Patent Reference 1, for example, has hitherto described this kind of lens barrel cam mechanism. That is, the Cited Patent Reference 1 described technologies relating to a light amount adjusting apparatus located in a light path of an optical system and a camera incorporating therein a light amount adjusting apparatus (hereinafter referred to a “first related-art example”. A camera according to this first related-art example includes an optical system having a first lens group of which light exit surface is formed as a concave surface and a second lens group including a convex surface on which light from the first lens group becomes incident and which can be magnified with its optical iris position between the first lens group and the second lens group. There are also included a filter apparatus having predetermined transmittance located behind the second lens group and which can be moved between the position to open an exposure opening and the position to shut the exposure opening and a control unit for controlling based on the magnified states of the optical system and shutter speeds whether the filter apparatus is to be moved to the position to shut the exposure opening. This camera according to the first related-art example is characterized in that, if the shutter speed becomes higher than a predetermined value in the state in which the filter apparatus is located at the position to open the exposure opening, then the filter apparatus is moved to the position to shut the exposure opening so that the camera becomes able to take a picture at a lower shutter speed.
According to the camera having the above-mentioned arrangement described in the Cited Patent Reference 1, there can be achieved effects in which the arrangement of a shutter diaphragm can be optimized, the occurrence of a shutter light amount difference of the shutter diaphragm can be decreased, more suitable exposure can be executed and the size of the camera can be miniaturized (paragraph [0094] in the Japanese patent specification of the Cited Patent Reference 1).
Also, Cited Patent Reference 2 has described another example of this kind of the lens barrel cam mechanism according to the related art. The Cited Patent Reference 2 has described technologies concerning a collapsing/extending lens apparatus having a zooming function (hereinafter referred to as a “second related-art example”. The lens apparatus according to the second related-art example includes a lens holding frame for holding a lens and which has a cam follower protruded therein and a cam cylinder having a cam groove, engaged with the cam follower of the lens holding frame, formed on the inner peripheral surface and which is rotated around a lens optical axis wherein a vertical surface vertical to the inner peripheral surface of the cam cylinder and an inclined surface inclined relative to the vertical surface are formed on the side surface of the cam groove.
According to the lens apparatus having the above-mentioned arrangement described in the Cited Patent Reference 2, since the vertical surface vertical to the inner peripheral surface of the cam cylinder and the inclined surface inclined relative to this vertical surface are formed on the side surface of the cam groove, the vertical surface may act as a stopper surface relative to the vertical surface. Thus, it is possible to prevent the cam follower from being disengaged from the cam groove (paragraph [0096] of the Japanese patent specification).
[Cited Patent Reference 1] Japanese unexamined patent publication No. 2004-252367
[Cited Patent Reference 2] Japanese unexamined patent publication No. 2002-267917
However, in any case of the aforementioned first and second related-art examples, the cam groove was formed on the inner peripheral surface of the cam frame (cam cylinder) and the like, a cam follower of a linearly movable frame guided linearly was engaged with the cam groove so as to become slidable, a drive gear was meshed with a gear portion provided on one side of a rotary axis direction of a cam ring and the drive gear was rotated by power from a power source to rotate the cam ring, whereby the linearly movable frame could be moved forward or moved backward in response to the rotation direction of the cam ring. As a result, a sufficiently large movement amount of the linearly movable frame in the rotary axis direction may not be obtained.
It is customary that, in this kind of the lens barrel cam mechanism, the maximum movement amount of the linearly movable frame is determined by the length of the rotary axis direction of the cam groove provided on the cam ring. While a gear portion is provided on one side of the rotary axis direction of this cam ring, the gear portion should be formed so as not to interfere with the cam groove. Further, the length of the rotary axis direction of the cam groove is also limited by the length of the rotating direction of the gear portion. For this reason, the length of the rotary axis direction of the cam ring should be selected to be such one that can secure a length which results from adding a width of the gear portion to the length of the rotary axis direction of the cam groove.
However, in lens barrels for use with recent digital cameras, particularly, in lens barrels having a zooming function, to increase a magnification of an optical system has been in increasing demand and hence it is necessary to increase an amount in which a linearly movable frame such as a lens frame may be moved in the optical axis direction. On the other hand, miniaturization of the lens barrel itself also has been in increasing demand. As a consequence, it becomes necessary to provide a mechanism by which the movement amount of the optical axis direction of the linearly movable frame can be increased without increasing the length of the rotary axis direction of the cam ring.